Acoustical, or ceiling, panels are well known for providing a finished appearance to a ceiling area and also providing a sound absorbent surface where needed. Ideally, the panels combine acoustic absorbency with durability for long life. Mineral wool is commonly used because it provides a porous fibrous structure for absorbing sound. Other common materials used in the manufacture of ceiling panels include fiberglass, expanded perlite, clay, gypsum, stucco, calcium carbonate and paper fiber.
Many ceiling panels are made in a manner similar to the process used to make paper or fiberboard. In this water-felting process, an aqueous dispersion of the fibers, aggregates, binders, and other additives is dispensed onto a porous surface or wire where the furnish is dewatered, both by gravity and by vacuum suction. The wet mat is dried in a convection oven and then cut into desired lengths. If desired, the surface is painted to produce a finished panel. An example of such a panel is the AURATONE® ceiling tile made by USG Interiors (Chicago, Ill.).
Another process for making ceiling panels is by casting, as described in U.S. Pat. No. 1,769,519. A composition of mineral wool fibers, fillers, colorants, a binder such as cooked starch and water is placed in trays covered with paper or paper-backed foil. The composition is then screeded with a forming plate to the desired thickness. A decorative surface, such as an embossed pattern, is obtainable by imparting a pattern into the surface of the cast material by use of a screed bar or a patterned roll. ACOUSTONE® ceiling tile by USG Interiors (Chicago, Ill.) is an example of such a cast panel.
Both of these methods of making ceiling panels are relatively expensive because they utilize large amounts of water and energy. Hygroscopic binders, such as paper or starch, result in panels that are susceptible to sag. Sagging of the panel can be accentuated when the panel supports insulation or other loads or when subjected to high levels of humidity and temperature.
Gypsum panels are less prone to sag and are manufactured efficiently in a high-speed process. However, gypsum is heavy and it lacks acoustical absorbency. It is currently adaptable for use as acoustical ceiling panels by including holes in the panels and positioning a sound-absorbing backing on the back of the perforated panel. While the holes provide some weight reduction and sound absorbance, they are not accepted by consumers as being aesthetically pleasing.
Another gypsum panel having an acoustical layer is described in U.S. Patent Publication No. 2004/0231916. One embodiment of this panel has an acoustical layer of foamed gypsum formed on a backing sheet for strength. The panel is lightweight, sag resistant and aesthetically pleasing.
This layered gypsum panel has a disadvantage. During installation, the panels are cut to fit the shape of the ceiling and/or the openings in a structure that holds them in place, such as a ceiling grid. Cutting through the composite of gypsum generates fine airborne dust that takes a long time to settle due to the small particle size of the dust. The fineness of the dust allows it to travel long distances before finally settling out. The cutting action can create nuisance dust which can reduce visibility, as well as get into the eyes, ears and nose. After settling out, there is a huge mess to clean up since the fine dust can permeate doors and other barriers, and can settle some distance from where the cutting takes place.
Dust reduction during sanding, cutting and abrading has become an important feature for gypsum products. U.S. Pat. No. 6,863,723 to 3M suggests reduction of dust by the addition of one of several dust reducing agents to gypsum containing products. U.S. Pat. No. 6,673,144 to United States Gypsum Company features a joint compound having polyethylene glycol, where the polyethylene glycol is a solid at room temperature. A sprayable plaster that utilizes polyethylene glycol as an internal binder produces less fine dust when machined in U.S. Pat. No. 6,355,099. None of these references disclose the addition of polyethylene glycol to an acoustic panel.